JP3194577B2 - Method for producing needle-like magnetic metal particles containing iron as a main component - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an SFD (Switching Field Dist) having a high coercive force and a large saturation magnetization and being fine particles.
The present invention relates to a method for producing acicular metal magnetic particles containing iron as a main component and having excellent ribution.

[Conventional technology]

In recent years, as the size and weight of magnetic recording / reproducing devices have been reduced, the need for higher performance for magnetic recording media such as magnetic tapes and magnetic disks has been increasing. That is, high-density recording, high output characteristics, particularly, improvement in frequency characteristics and reduction in noise level have been required. In order to satisfy various demands for magnetic recording media, magnetic particles used in the production of magnetic recording media must have high coercive force and large saturation magnetization,
D. must be excellent.

Therefore, in recent years, magnetic particle powders suitable for high-output and high-density recording, that is, magnetic particle powders having high coercive force and large saturation magnetization, have been actively developed, and the first magnetic particle powder having such characteristics has been developed. Heating the needle-like hydrous ferric oxide particles or the needle-like hydrous ferric oxide particles obtained by oxidizing a neutralized precipitate of an iron salt and an alkaline aqueous solution such as an alkali hydroxide or an alkali carbonate. The acicular hematite particles, which were fired and laughed, were used as starting material particles, and the starting material particles were reduced by heating in a reducing gas to obtain acicular metal magnetic particles containing iron as a main component. Acicular crystalline magnetic particle powder containing iron as a main component and obtained by forming an oxide film on the surface is known and has been put to practical use.

Next, the noise level of the magnetic recording medium depends on the particle size of the acicular metal magnetic particle powder containing iron as a main component used in the production of the magnetic recording medium and the primary particles constituting one particle, that is, X It is widely known that there is a close relationship with the size of the line particle size, and the smaller the size of the particle size and the size of the X-ray particle, the lower the noise level tends to be.

Further, in order to increase the output of a magnetic recording medium, in addition to the above-mentioned improvement of the magnetic properties, it is required that the SFD of the acicular metal magnetic particles containing iron as a main component is further excellent.

When the relationship between the SFD of a magnetic recording medium and the recording / reproducing output is represented by a graph as described in JP-A-62-26821, the recording / reproducing output increases linearly as the SFD value decreases. This indicates that the use of magnetic particle powder with a small SFD increases the recording / reproducing output. That is, in order to improve the recording / reproducing output of the magnetic recording medium, the SFD of the magnetic particle powder is desirably small, and an SFD of 0.6 or less is required to obtain an output higher than usual.

In general, the finer the particle size of the acicular metal magnetic particle powder containing iron as a main component, the better the coercive force,
The noise level of magnetic recording media tends to decrease,
Since the surface activity of the particles becomes very large, if an oxide film is formed by a usual method, it reacts rapidly with oxygen in the air, and the ratio of the oxide film to the particles relatively increases, and the oxide film becomes rougher. And it becomes uneven. As a result, the magnetic properties, especially the saturation magnetization, are reduced.
At the same time, a coercive force distribution occurs, which causes a decrease in SFD. This phenomenon tends to occur more easily as the particle size becomes finer.The saturation magnetization value of the needle-shaped metal magnetic particle powder containing iron as a main component after forming an oxide film usually has a particle size of 0.3. about 150 emu / g at about μm,
It is about 125 emu / g at about 0.2 μm.

Conventionally, needle-like metal magnetic particles containing iron as a main component after reduction with the aim of improving the oxidation stability of needle-like metal magnetic particles containing iron as a main component and an organosilicon compound in a gaseous state The method of contacting is reported in JP-A-60-154502, but in this method, a silane compound having a strong hydrolyzability is used, and the hydrolysis reaction is promoted by actively presenting water. As a result, a hydrolysis reaction rapidly progressed, and thus acicular metal magnetic particles containing iron as a main component and sufficiently satisfying the above characteristics could not be obtained.

[Problems to be solved by the invention]

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a high-coercive force and a large saturation magnetization, and further, are mainly composed of iron, which is a fine particle and has an excellent SFD. It is an object of the present invention to provide a method for producing acicular metal magnetic particle powder.

[Means for solving the problem]

The object of the present invention is to provide a needle-like hydrous ferric oxide particle having a major axis diameter of 0.1 to 0.5 μm and an axial ratio (major axis diameter / minor axis diameter) of 3 or more, or The needle-like hematite particles obtained by heating and calcining the diiron particles are heated and reduced in a reducing gas to obtain needle-like metal magnetic particles having a major axis of 0.2 μm or less and containing iron as a main component. At least one kind of a silicone compound monomer represented by the following general formula (I) is brought into contact with the acicular metal magnetic particles in a gaseous phase at 70 ° C. or lower under an inert atmosphere, and the particle surface is previously prepared from the silicone compound monomer. After coating with the formed polymer, the supply of the silicone compound monomer was stopped, and then the excess silicone compound was removed from the system by heating to a temperature of more than 70 ° C. and 80 ° C. or less under an inert atmosphere. 100 ~ 120 ℃
A needle-like metal comprising iron as a main component, characterized in that the polymer coating layer is densified by heating to a temperature of 3 ° C., and then treated under an oxygen-containing inert atmosphere to form an oxide film on the particle surface. This is achieved by a method for producing magnetic particle powder.

(R ¹ HSiO) _a (R ² R ³ SiO) _b (R ⁴ R ⁵ R ⁶ SiO _1/2 ) _c (I) (where R ¹ , R ² , R ³ , R ⁴ , R ⁵ or R ^{And 6} is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with at least one halogen atom.
Or b is 0 or an integer of 1 or more, and c is 0
Or 2. However, when c is 0, the sum of a and b is an integer of 3 or more. [Operation] First, the most important point in the present invention is that the various properties possessed by the needle-shaped metal magnetic particles mainly composed of iron immediately after reduction are maintained at a high level even after being taken out into the air. It is a fact that you can do it.

The reason for this is that the needle-like metal magnetic particles containing iron as a main component immediately after reduction are coated under an inert gas atmosphere with a polymer formed from a specific silicone compound monomer on the particle surface. After heating to a temperature of more than 70 ° C. and 80 ° C. or less under an inert atmosphere to remove excess monomers from the system, heating to 100 to 120 ° C. densifies the polymer coating layer, and then contains oxygen. When an oxide film is formed on the particle surface by treatment under an inert atmosphere, a fine and, particularly, particle size of 0.2 μm or less is caused due to formation of a uniform and dense polymer film. It is believed that the surface activity of the acicular metal magnetic particles containing iron as a main component can be sufficiently suppressed. Therefore, in the present invention, it is considered that a thin and dense and uniform oxide film could be formed on the particle surface as much as possible.

 Hereinafter, the present invention will be described in more detail.

As the starting material particles in the present invention, a major axis diameter of 0.1 to
Needle-crystal hydrated second particles having a diameter of 0.5 μm, preferably 0.1 to 0.3 μm, and an axial ratio (major axis / minor axis) of 3 or more, preferably 5 or more are used. Here, the acicular crystal refers to particles having an axial ratio (major axis diameter / minor axis diameter) of 3 or more, and includes needle-shaped particles as well as spindle-shaped, rice-grained, and elliptical particles.

Further, as the starting material particles in the present invention, needle-like hematite particles obtained by heating and firing needle-like hydrous ferric oxide particles can be used, if necessary. The heating and firing temperature in this case is preferably 250 to 850 ° C.,
In order to maintain and retain the shape of the starting material particles, it is preferable to heat and sinter at a high temperature of 350 to 700 ° C. to densify the acicular hematite particles.

The starting material particles in the present invention, other than Fe such as Al, Ni, Co, B, Zn, P, which are usually used to improve various properties of the acicular metal magnetic particle powder containing iron as a main component. A different element may be present.

In the present invention, needle-like ferric hydrate particles or needle-like hematite particles are reduced by heating in a reducing gas, and the reduction temperature is preferably 300 to 500 ° C. If the temperature is lower than 300 ° C., the progress of the reduction reaction is slow, and it takes a long time. Also, 50
When the temperature exceeds 0 ° C., the reduction reaction proceeds rapidly, so that deformation of the particle form and sintering between the particles and the particles are easily caused.

In the present invention, the needle-shaped metal magnetic particles mainly composed of iron immediately after reduction are brought into contact with the silicone compound monomer represented by the general formula (I) in an inert gas atmosphere in a gas phase. It is necessary to coat the particle surface with a polymer formed from a specific silicone compound monomer.

Two representative groups of the silicone compound monomers represented by the general formula (I) are represented by the following general formula (II) or (III)
Indicated by In the first group, c = 0 in the general formula (I).
The following general formula (II) (R ¹ HSiO) _a (R ² R ³ SiO) _b (II) (wherein R ¹ , R ² , R ³ , a and b are the same as those described above) But preferably each of R ¹ , R ² or R ³ is at least 1
1 to 10 carbon atoms which may be substituted with halogen atoms
Wherein the sum of a and b is an integer of 3 or more). Representative examples of this compound are as follows.

The above compounds (A) and (B) can be used alone or in the form of a mixture thereof.

In each of the formulas of the compounds (A) and (B), n (or a + b) is preferably 3 to 7, respectively. n
Since the boiling point decreases as the value of (or a + b) decreases, the amount of evaporation and adsorption on the powder increases. In particular, when n (or a + b) is an integer of 3 or 4, it is particularly suitable because it is easy to polymerize due to its steric properties.

Specific examples of the cyclic silicone compound represented by the general formula (II) include dihydrogen hexamethylcyclotetrasiloxane, trihydrogenpentamethylcyclotetrasiloxane, tetrahydrogentetramethylcyclotetrasiloxane, dihydrogenoctamethylcyclopentasiloxane. Examples include siloxane, trihydrogenheptamethylcyclopentacycloxane, tetrahydrogenhexamethylcyclopentasiloxane, and pentahydrogenpentamethylcyclopentasiloxane.

The second group of the silicone compound monomers represented by the general formula (I) corresponds to the case where c = 2 in the general formula (I), and the following general formula (III) (R ¹ HSiO) _a (R ² R ³ SiO) _b (R ⁴ R ⁵ R ⁶ SiO _1/2 ) _c (III) wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , a and b are as defined above. The same, but preferably, each of R ^{1 to} R ⁶ has 1 carbon atom which may be substituted with at least one halogen atom.
~ 10 hydrocarbon groups. ] It is a linear silicone compound represented by these. As a typical example of this compound, the following general formula (D) Can be mentioned.

Specific examples of the linear silicone compound represented by the general formula (III) include 1,1,1,3,5,7,7,7-octamethyltetrasiloxane, 1,1,1,3,5,7 , 9,9,9-Nonamethylpentasiloxane and 1,1,1,3,5,7,9,11,11,11-decamethylhexasiloxane.

The contact of the particles of the present invention with the silicone compound monomer represented by the general formula (I) in an inert gas atmosphere in a gas phase is preferably performed using a closed container at a temperature of 70 ° C. or less. Is 200 mmHg or less, more preferably 100 mmHg
A method in which the vapor of the silicone compound monomer is brought into contact with the particle surface in a molecular state under the following pressure, at 70 ° C.
This is performed by a method of supplying a mixed gas of the silicone compound monomer and the carrier gas to the particles under the following temperature and in an inert gas atmosphere.

The coating amount of the silicone compound polymer in the present invention is 0.1 to 10% by weight in terms of Si with respect to Fe in the particles to be treated,
Preferably, it is 0.2 to 8.0% by weight. If the content is less than 0.1% by weight, the effect of suppressing the surface activity of the particles is not sufficient, so that the oxide film becomes thicker, moreover, tends to be coarse and non-uniform, and the magnetic properties, especially the saturation magnetization, decrease.
SFD also tends to get worse. If it exceeds 10% by weight, the saturation magnetization of the iron-based acicular metal magnetic particles obtained mainly due to the increase in the components that do not contribute to the magnetic properties tends to decrease.

In the present invention, the particles are brought into contact with the silicone compound monomer represented by the general formula (I) in a gas phase to cause a polymerization reaction of the silicone compound monomers on the particle surface. Generally, when thermal polymerization is caused, it is impossible to form a uniform and dense coating. Furthermore, when the polymerization is carried out in the presence of a catalyst, the polymerization mainly occurs around the catalyst, so that it is impossible to uniformly coat only the surface of the particles.

It is presumed that the polymer formed from the silicone compound monomer represented by the general formula (I) coated on the particle surface is a silicone compound represented by the following general formula (IV).

(R ¹ SiO _3/2 ) _a (R ² R ³ SiO) _b (R ⁴ R ⁵ R ⁶ SiO _1/2 ) _c (IV) (where R ¹ , R ² , R ³ , R ⁴ , R ⁵ or R ⁶ is a hydrogen atom, a hydroxyl group, or a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with at least one halogen atom.
A is an integer of 1 or more, b is 0 or an integer of 1 or more, and c is 0 or 2. However, when c is 0, a
And b is an integer of 3 or more. The structure of the polymer represented by the general formula (IV) includes, for example, two types described below. That is, in a polymer of a silicone compound in which polymerization occurs by cleavage and recombination of a siloxane bond (-Si-O-Si-), -Si-
It has only a chain structure of O-Si- units, while the polymerization is H ₂ O
Or hydrosilyl bond in the presence of O ₂ (Si-H)
If they are caused by a cross-linking reaction: Derived from A polymer formed from a specific silicone compound monomer will include a network having units.

In this case, the polymer of the silicone compound having a network structure (hereinafter referred to as “network structure polymer”) accounts for 20% or more of all Si atoms. It is preferably converted to a unit. The content of this unit can be determined from the IR absorption of a methyl group in the formed silicone compound.

Further, when the content of this unit increases and the network structure develops, the silicone compound is released by heating and releases only methane without depolymerization to form a Si oxide. This state can be confirmed by pyrolysis gas chromatography.

In the present invention, a compound having another structure derived from the silicone compound monomer represented by the general formula (I) may be present.

In the present invention, the particle surface of the needle-shaped metal magnetic particles mainly composed of iron immediately after reduction is coated with a polymer formed from the silicone compound monomer represented by the general formula (I), and then the silicone compound monomer is coated. Is stopped, and then heat treatment is performed under an inert atmosphere to remove excess silicone compound from the system. The heat treatment in that case is performed at a temperature of more than 70 ° C and 80 ° C or less.

In the present invention, after the excess silicone compound is removed from the system, the polymer coating layer formed is densified by heating at 100 to 120 ° C. in an inert atmosphere.

The formation of the oxide film in the present invention can be carried out by a method in which after the polymer coating layer is densified, the oxygen content in the inert gas is gradually increased and finally gradually oxidized with air. If necessary, other known methods,
For example, a method of dipping in an organic solvent such as toluene may be combined. However, when forming an oxide film, it is preferable to control the air content, the amount of air flow, and the time of air flow, and to perform the oxidation under the mildest possible conditions.

The needle-shaped metal magnetic particle powder containing iron as a main component obtained by the present invention has a coercive force of 1500 Oe or more and a saturation magnetization of 155 emu / g.
As described above, the major axis is 0.2 μm or less and the SFD is 0.35 or less. However, if the major axis is too small, it is difficult to obtain a high coercive force and a large saturation magnetization. Also,
The particle size is preferably 175 ° or less.

〔Example〕

Next, the present invention will be described with reference to Examples and Comparative Examples. In addition, the major axis and the axial ratio (major axis diameter / minor axis diameter) of the particles in the following Examples and Comparative Examples are shown by the average value of numerical values measured from an electron micrograph.

The magnetic properties of the needle-shaped metal magnetic particle powder containing iron as the main component and the magnetic tape are as shown in "Vibrating sample magnetometer VSM-3S-15".
(Manufactured by Toei Kogyo Co., Ltd.) using an external magnetic field of 10 kOe.

Measurement of SFD, using a sheet-like sample piece obtained by the following method, using a differentiation circuit of the magnetometer,
The derivative curve of the coercive force was obtained, the half width of this curve was measured, and this value was obtained by dividing the value by the coercive force of the peak value of the curve.

Preparation of sheet-shaped sample pieces The following [A] was placed in a 140 cc glass pin and mixed and dispersed for 6 hours, and the prepared magnetic paint was applied to a 25 µm thick polyethylene terephthalate film to a thickness of 50 µm using an applicator. And then dried in a magnetic field of 5 kGauss.

[A]: 100 parts by weight of a kneaded product (100 parts by weight of a metal magnetic powder containing iron as a main component and 50 parts of a vinyl chloride / epoxy copolymer having a sodium sulfonate group (as a 30% by weight solution of cyclohexanone) in an amount of 88 cc)
And kneaded for 45 minutes using a Plastmill. ) 1mmφ glass beads 530 parts by weight Cyclohexanone 50 parts by weight Methyl ethyl ketone 57 parts by weight Toluene 57 parts by weight The X-ray particle size (D ₁₁₀ ) is the size of crystal grains measured by X-ray diffraction, perpendicular to the (110) crystal plane. The thickness was expressed by the thickness of crystal grains in various directions, and the measurement was represented by a value calculated using the following general formula based on a crystal grain size measurement method.

Where β = half-width of the true diffraction peak k = Scherrer constant (0.9) λ = wavelength of X-ray (1.935 °) θ = diffraction angle Example 1 Long axis 0.22 μm, axial ratio (long axis diameter / short axis) Co) which is 12)
A long axis 0.22 μm obtained by heating and calcining spindle-shaped goethite particles having an oxide film containing Al and B formed on the particle surface at 350 ° C. in the air, and having an axial ratio (long axis diameter / short axis) was charged shaft diameter) is 12 needles hematite particles 300g during retort vessel 3, while rotated aerated at a rate per minute 35 H ₂ gas, and reduced with reducing temperature 390 ° C..

Then, while flowing nitrogen gas into the retort container, 60
After cooling to 50 ° C., 50 g of tetramethylcyclotetrasiloxane (n = 4 in the general formula (A)) separately prepared and maintained at 60 ° C. was bubbled with nitrogen gas in a container, and the mixed gas was retorted as described above. It was fed into the container for 2 hours.

Thereafter, the supply of the mixed gas was stopped, and the mixture was heated at 80 ° C. for 2 hours to remove excess silicone compound from the system. Furthermore, the temperature was raised to 120 ° C., and the formed silicone compound was densified for 2 hours.

Subsequently, while nitrogen gas was passed, air was blown at a rate of 0.2 l / min for 30 minutes. After air ventilation, acicular metal magnetic particles containing iron as a main component were taken out into the air. At this time, the amount of the silicone compound polymer was 1.51% in terms of Si with respect to Fe as a result of analysis by elemental analysis.

Further, the needles magnetic metal particles containing iron as a main component was analyzed by infrared absorption spectrum results of the 1260 cm ^-1 Si-
The absorption of the CH ₃ group was shifted to 1270 cm ⁻¹ , indicating that oxygen reacted with the Si—H group and changed to Si—O. Also,
As a result of pyrolysis gas chromatography at 590 ° C., since only methane was produced, it was confirmed that tetramethylcyclotetrasiloxane was cross-linked and polymerized to form a network polymer. From this, it was confirmed that the particle surface of the acicular metal magnetic particles containing iron as a main component was coated with a polymer having a network structure.

As a result of electron microscopic observation, the long axis of the obtained acicular metal magnetic particles containing iron as a main component was 0.15 μm.
The linear particle size (D ₁₁₀ ) was 160 °.

The coercive force is 1630 Oe, the saturation magnetization is 161.0 emu / g, SF
D. was 0.297.

Examples 2 to 5, Comparative Examples 1 to 5 Types of needle-shaped hydrous ferric oxide particles, heating and sintering temperature, heating and reduction temperature and time, and type of silicon compound, Si / Fe
Except for changing the amount, the processing conditions, and the heat treatment conditions as shown in Table 1, the same procedure as in Example 1 was carried out to prepare acicular metal magnetic particles containing iron as a main component.

The main manufacturing conditions at this time are shown in Table 1, and various characteristics of the acicular metal magnetic particles containing iron as a main component are shown in Table 2.

However, the coating of the polymer formed from the specific silicone compound monomer on the particle surface in Example 5 was performed by the following method. That is, the needle-shaped crystalline magnetic particles containing iron as a main component after reduction are taken out into a vessel purged with nitrogen, and left in a nitrogen-purged closed thermostat together with 1.8 g of tetramethylcyclotetrasiloxane, and then 200 mmH
It was carried out by treating at 70 ° C. for 5 hours under a pressure of g.

In Comparative Example 4, the excess silicone compound to be removed after the supply of the mixed gas was stopped was removed at 80 ° C.
A needle-shaped metal magnetic material containing iron as a main component in the same manner as in Example 3 except that the formed silicone compound was densified for 2 hours by immediately raising the temperature to 120 ° C. without performing the heat treatment for a long time. A particle powder was prepared.

In Comparative Example 5, needle-like metal magnetic particles containing iron as a main component were prepared in the same manner as in Example 3 except that the formed silicone compound was not densified.

As is evident from Table 2, the iron-based acicular metal magnetic particles obtained by the present invention were fine particles and were very excellent in all values of coercive force, saturation magnetization and SFD.

〔The invention's effect〕

According to the present invention, a high coercive force of 1500 Oe or more and 155 emu / g
With the above large saturation magnetization, and the major axis is 0.2 μm
It was possible to provide acicular metal magnetic particle powder containing iron as a main component having an SFD of 0.35 or less. The acicular metal magnetic particle powder containing iron as a main component obtained by the present invention is suitable as the most demanded magnetic particle powder for high density recording, high output, and low noise level.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Ogawa 1050 Nippa-cho, Kohoku-ku, Yokohama, Kanagawa JP-A-63-113082 (JP, A) JP-A-60-36603 (JP, A) JP-A-63-222404 (JP, A) JP-A-58-174509 (JP, A) JP-A-61-22428 (JP, A) JP-A-63-26821 (JP, A)

Claims (1)

(57) [Claims] A needle-containing hydrous ferric oxide particle having a major axis diameter of 0.1 to 0.5 μm and an axial ratio (major axis diameter / minor axis diameter) of 3 or more. The needle-shaped hematite particles obtained by heating and sintering the particles are heated and reduced in a reducing gas to obtain needle-shaped metal magnetic particles having a major axis of 0.2 μm or less and containing iron as a main component. At least one of the silicone compound monomers represented by the following general formula (I) is brought into contact with the crystalline metal magnetic particles in a gas phase at 70 ° C. or lower under an inert atmosphere, and the particle surface is previously formed from the silicone compound monomers. After coating with the polymer, the supply of the silicone compound monomer was stopped, and the mixture was heated at a temperature of more than 70 ° C. and 80 ° C. or less in an inert atmosphere to remove excess silicone compound from the system. Heating to a temperature of 120 ° C. to form a coating layer of the polymer , And then treating it in an oxygen-containing inert atmosphere to form an oxide film on the surface of the particles. (R ¹ HSiO) _a (R ² R ³ SiO) _b (R ⁴ R ⁵ R ⁶ SiO _1/2 ) _c (I) (where R ¹ , R ² , R ³ , R ⁴ , R ⁵ or R ^{And 6} is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with at least one halogen atom.
Or b is 0 or an integer of 1 or more, and c is 0
Or 2. However, when c is 0, the sum of a and b is an integer of 3 or more. )